The present invention is in the field of electronic cooling.
This invention relates to a heat sink apparatus useful in electronic devices. More specifically, this invention relates to removing heat from microelectronics that are useful in computerized devices.
The heat removal problem has become an important factor in the advancement of microelectronics due to both drastically increased integration density of chips in digital devices as well as an increased current-voltage handling capability of power electronic devices. The task of removing a large amount of dispersed heat from a constrained, small space is often beyond the capability of conventional cooling techniques. New methods with heat removal capabilities at least one order larger than that of conventional ones are therefore required.
The present invention is based on a two-layer micro-channel heat sink design. Micro-channel heat sink has been studied and tested as a high performance and compact cooling scheme in microelectronics cooling applications. It is shown that the thermal resistance as low as 0.03xc2x0 C./W is obtainable for micro-channel heat sinks, which is substantially lower than the conventional channel-sized heat sinks. Design factors that have been studied include coolant selection (air and liquid coolant), inclusion of phase change (one phase and two phase), and structural optimization.
One drawback of micro-channel heat sink is the relatively higher temperature rise along the micro-channels compared to that for the traditional heat sink designs. In the micro-channel heat sink, the large amount of heat generated by the semiconductor chips is carried out from the package by a relatively small amount of coolant so the coolant exits at a relatively high temperature.
This undesirable temperature gradient is an important consideration in the design of an electronic cooling scheme. A large temperature rise produces thermal stresses in chips and packages due to the coefficient of thermal expansion (CTE) mismatch among different materials thus undermining device reliability. Furthermore, a large temperature gradient is undesirable for the electrical performance since many electrical parameters are adversely affected by a substantial temperature rise. For instance, in power electronic devices electrical-thermal instability and thermal breakdown could occur within a high temperature region.
In the one-layered micro-channel heat sink design, increasing the pressure drop across the channels can control bulk temperature rise along the channels. A larger pressure drop forces coolant to move faster through the channel, thereby requiring more powerful pumping power supply, generating more noise, and requiring bulkier packaging. Two-phase micro-channel heat sink is an alternative method for eliminating the temperature variations, in which the utilization of latent heat can achieve a uniform temperature profile on the heating surface. However, a two-phase scheme can have several drawbacks, such as a complicated structure and a much larger pressure drop required for the gas-liquid mixture to flow inside the minute conduits.
The present invention reduces the undesired temperature variation in the streamwise direction for the micro-channel heat sink by a design improvement, instead of increasing the pressure drop. The design in the present invention is based upon stacking two layers of micro-channel heat sink structures, one atop the other, with coolant flowing in the opposite direction in each of the micro-channel layers. For such an arrangement, streamwise temperature rise for the coolant and the substrate in each layer may be compensated through conduction between the two layers, resulting in a substantially reduced temperature gradient. The flow loop can be similar to the one designed for the one-layered micro-channel heat sink, except that the flow loop should bifurcate to allow the coolant to flow from opposite, or the same directions, into each of the channels.
In the present invention, the thermal performance of the proposed two-layered micro-channel heat sink is examined numerically using a finite element method and optimization issues for design parameters are addressed as well. Although a one-layered micro-channel heat sink has been extensively studied, the proposed two-layered structure concept has never been reported.
Although described with respect to the fields of electronics and microelectronics, it will be appreciated that similar advantages of a high performance and compact cooling scheme may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes heat sinks, heat sink devices, and heat sink systems. The present invention may also be used as a heat source, a heat source device, and in heat source systems, in accordance with methods of heat transfer known to one skilled in the art. The invention also includes machines or electronic devices using these aspects of the invention. The present invention may also be used to upgrade, repair or retrofit existing machines or electronic devices or instruments of these types, using methods and components known in the art.
In broadest terms, the two-layered micro-channeled heat sink (or heating) device of the present invention comprises: (1) a first layer comprising a duality of micro-channels in thermal contact with a heat-generating (or in the case of use as a heating device, with a heat absorbing) surface, (2) a second layer of micro-channels in thermal contact with the first layer, and (3) a device for circulating a coolant (or heating fluid) through the first and second layers such that the coolant (or heating fluid) flows through the first and second layers in opposing directions (or in the same direction).
The heat sink (or heating device) may be made of any appropriate material consistent with its intended function as reflected in the present disclosure. For instance, the channel walls may be made of silicon. The system can be augmented by the addition of any related device, including a cooling (or heating) device, a heat exchange device, a coolant (or heating fluid) filter, a coolant (or heating fluid) reservoir, and a flow-generating device. Typically, the dimensions of the individual micro-channels should be less than one-sixteenth of an inch in height and width, and comparable to the size of the heat-generating (or heat absorbing) substrate in length. EDM is an example of a technique that may be used to create these micro-channels, among other methods of micro-machining known to one of ordinary skill in the art.
Also included in the present invention is, in broadest terms, an electronic device in thermal contact with a two-layered micro-channeled heat sink (or heat source) device, where the heat sink (or heat source) device comprises: (1) electronic circuitry capable of generating (or absorbing) heat; (2) a first layer comprising a duality of micro-channels in thermal contact with a heat-generating surface or surface to be heated, (3) a second layer of micro-channels in thermal contact with the first layer, and (4) a device for circulating a coolant (or heating fluid) through the first and second layers such that the coolant (or heating fluid) flows through the first and second layers in opposing directions (or in the same direction).
The heat sink (or heating device) in thermal contact with the electronic device may similarly be made of any appropriate material consistent with its intended function as reflected in the present disclosure, such as silicon. The system can also be augmented by the addition of a related device, such as a cooling (or heating) device, heat exchange device, coolant (or heating fluid) filter, coolant (or heating fluid) reservoir, or flow-generating device. The dimensions of the individual micro-channels should be less than one-sixteenth of an inch in height and width, and comparable to the size of the electronic circuitry in length.